This proposal is for the purchase of a Fluorescent Activated Cell Sorter (FACS) (Coulter Epic Model 753). The FACS will serve a group of investigators, mostly immunologists, based in the Clinical Sciences Research Building of the Washington University Medical Center. The investigators are from the Department of Pathology, Department of Surgery, Department of Medicine and Department of Pediatrics. The FACS will be housed in a laboratory of easy access to all investigators. Dr. Unanue will be responsible for the instrument and will be aided by a small committee made up of representatives from Medicine, Surgery and Pathology. The day to day operation will be under Dr. Kenneth Stone, who has long-term experience with cell sorters. The immunology projects that are described use the FACS either for analytical purpose, i.e., to classify and identify murine or human lymphoid cells or for preparative purpose, i.e., to purify and isolate a given cell type. The projects described are studying macrophage-lymphocyte interactions during antigen presentation, the interaction of cytolytic T cells with cells infected with viruses, the cellular basis of allograft rejection, the immunological response at the level of the gastrointestinal tract and, the molecular basis of phagocytosis, the human lymphocyte response to adenosine compounds. One non-immunological project involves cell cycle analysis of breast cancer cells. The justification for purchasing the instrument is the increased needs resulting from the growth of research, particularly immunology, in the clinical departments housed in the new clinical research facility.